A conventional filter assembly typically comprises a fully integrated tubular or cylindrical filter element and a cylindrical perforated core which are permanently affixed at their ends to end caps. In more detail, the filter element, which includes a filter medium, surrounds the rigid cylindrical core to establish a tubular or cylindrical configuration. Each of the axial ends of the core and the filter element are sealed to an end cap, which is formed as a unitary, one-piece structure. The end caps are secured to the core and the filter element by conventional attachment techniques, e.g., gluing, ultrasonic welding, fusion bonding, friction (spin) welding, etc. The particular method is selected based on the characteristics of the materials employed. The result is (1) a leak-proof seal between the end cap and the filter element to prevent bypass of unfiltered fluid and contamination the filtered fluid (filtrate) and (2) a filter element which is supported by the core against radially and axially directed forces.
In service, unfiltered fluid, e.g., a liquid or a gas, is directed through the filter element where the filter medium blocks, entrains, traps and/or otherwise removes particulates from the unfiltered fluid to provide a filtrate free of such particulates. Over time, the particulates foul the filter medium, which, in turn, causes an increased pressure differential (pressure drop) across the filter element. When the pressure drop becomes substantial, indicating significantly reduced flow rates, maintenance is required. Maintenance may take different forms. Most commonly, the filter assembly is removed, discarded, and replaced with a new filter assembly.
When disposing of the entire filter assembly, not only is the filter element discarded but also the filter core. However, the filter core merely serves to support the filter element and facilitate drainage rather than to remove particulates. It commonly is still viable and usable after the filter medium is fouled. Thus, discarding the filter core along with the filter element comprises unnecessary economic and environmental waste.
Recognizing the potential for reusing cores, some structures have been suggested to provide a reusable filter core with a replaceable filter element. Such structures usually provide for the replaceable filter element to be slipped onto the support core and clamped to the core with rings or other compression based appliances. Application of such appliances to the filter element compresses the underlying filter medium and results in disrupting uniform filtering characteristics and flow. Thus, the structural integrity and filtration performance of the filter element may be impaired. Furthermore, unless care is exercised, the filter medium can be damaged during the application of such hardware. If damaged, the filter element must be disposed of even prior to use.
For certain filtration situations, valve type structures for pressure relief, temperature sensitive flow control, filter by-pass, and the like, may be incorporated into an end cap assembly. Conventional reusable core type filter assemblies typically do not incorporate such valves and do not contemplate filter by-pass. In applications requiring continuous fluid flow through a filter element circulation is paramount. Thus, if the filter medium becomes fouled, inducing a significant pressure drop across the filter element, or some factor increases the back-pressure relative to the filter element, critical fluid flow may be disrupted in conventional reusable core type filter assemblies with potential for catastrophic failure.